why so many languages

wouldn't it be better if there was only one language like c++ or c#
then programmers could spend their time mastering that language
instead of re-learning the basics of another language every few years

What you see as motivation to work, and the desire to fit in with society,
is what makes you limited and uninspired: your goals are set in the beginning.
The precedence of your prior choices dictates your life.

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Nature is busy creating absolutely unique individuals, whereas culture has invented a single mold to which all must conform. It is grotesque.